Elevator and like apparatus



H. J. GRAHAM ELEVATOR AND LIKE APPARATUS Original Filed June 13, 1930 RECTIFIER 2 Sheets-Sheet l Inventor.- Harold J. Gram,

Aug. 14,- 1934.

H. J. GRAHAM 1,970,304

ELEVATOR AND LIKE APPARATUS Original Filed June 13, 1930 2 Sheets-Sheet 2 Patented Aug. 14, 1934 UNITED STATES,

PATENT OFFICE Application June 13, 1930, Serial No. 460,884 Renewed January 16, 1934 28 Claims. (o1. lea-29) My invention relates'to apparatus for moving a part to and from selected predetermined posi-.- tions, as, for example, for moving an elevator car from any of the floors of a building to any selected floor thereof and automatically stopping when it reaches the latter.

The invention will be best understood from the following description when read in the light of theaccompanying drawings of one embodiment 0 of the invention, the scope of which latter will be more particularly pointed out in the appended claims.

The drawings show a schematic wiring diagram of one form of apparatus constructed according to the invention for raising and lowering an elevator,

Fig. 1 showing a part of the wiring; and J ,Fig. 2 showing the remainder of the wiring; these figures being so drawn that the wires ter- Q minating at the right hand side of Fig. 1 are continued at the left hand side ofFig. 2. I Referring to the drawings, the elevator car '1 is arranged in a shaft 3, and is suspended by, a cable 5 inv any suitable manner known to the .25 art, so that the elevator may be raised and lowterial with which slidably contacts a contactmember 11 carried by the car in insulated relation .35 thereto. Connected in parallel with the resistance strip 9 to a source of electromotive force, the latter herein exemplified by the secondary winding of. a step-down transformer 13, is a tapped resistance 15, the ends of the latter being connected to .40 the terminals of the transformer secondary by leads 1'7 and to the ends of the resistancestrip 9 by leads 19. As shown, the contact 11 is connected by a lead 21 to the movable brush arm- 23 of a multi-point switch comprising a plurality of circumferentially arranged spaced contacts 25 each connectedhy a. corresponding lead 27 to a tap on the resistance 15. r x

. It will be observed that, as above described, the two portions of the strip 9'respective1y above and below the contact 11 on the elevator car together constitute two resistances in series, and that likewise the tapped resistance 15 constitutes a number of resistances in series and, further, that these two sets ofresistances arecollectively connected in series-parallel with the source of electro-motive force, while the lead 21 connecting the brush arm 23 to the contact 11 is bridged across opposite sides of this system of resistances. This forms, in effect, a so-called Wheatstone-bridge, the potential diiference across the bridge circuit being varied as the car is raised or lowered. Conveniently, the resistances at 15 are so proportioned that, if the arm 23 is adjusted to a given contact 25, the potential across the bridge circuit will be zero when the car reaches a given floor. For convenience, the contacts 25 have been given legends indicating the floor to which the car must travel to make the potential across the bridge circuit zero when the brush arm.23 is set to the corresponding contact. The legends having the prefix U indicate the positions of the brush arm for moving the cars up to a given floor, and those having the prefix D down to a given floor.

It will be understood by those skilled in the art that when an alternating current source of electromotive force is employed for energizing a Wheatstone-bridge, the resistances may be other than so-called direct current resistances, that is to say, instead of direct current resistances, inductances for example may be employed, an inductance, as will be understood, having a resistance commonly termed impedance which for alternating currents is measured in ohms, as is likewise the resistance of a direct'current resistance in an alternating current circuit. Conance 15, provided the resistances connected to the same side of the line in each case are taken as the numerator (or denominator) of the fraction representing the ratio. If this difference is algebraically positive the car will move in one direction, and if algebraically negative will move in the opposite direction. When the arithmetical difference between the two ratios approaches zero the current in the bridge circuit approaches zero.

Herein the brush arm 23 is fixedly mounted on a shaft 29 in insulated relation thereto, said shaft being arranged to be rotated by a mo or schematically indicated at 31 in Fig. 2, this shaft also lia v ng thereon the operating parts of a reverse switch 32 for controlling the direction of movement of the elevator car, a release controlling switch 33 for the brush arm 23, and a selector 35 for determining the position of said brush arm.

Herein, for causing actuation of the controller motor 31, and for initiating operation of the elevator hoisting motor 7, each floor of the building is provided with one or more push buttons 3'1, the latter, in a manner hereinafter described, being connected in parallel with a group of corresponding push buttons 39 on the car to leads 41 and 43 energized by a suitable source of electro-motive force. For convenience, the leads which connect with the movable contacts of the push buttons 37 and 39 are provided with legends corresponding to the legends on the switch contacts 25 to which the taps of the resistance 15 are connected. As will be understood by those skilled in the art, the various leads brought into the elevator car are arranged in form of a cable.

The selector 35, hereinbefore referred to, comprises an arm 45 secured to the shaft 29, with which arm cooperates a plurality of electro-magnetically operated stops 47, the latter provided with actuating coils 49. As shown, one coil 49 is provided for each pair of push buttons 37, 39, the coils being marked with legends corresponding to the push buttons. Herein, the movable contact of each push button 37 is connected to the movable contact of the corresponding push button 39 by a lead 50, the latter being connected by a lead 51 to a terminal of the correspondingly marked coil 49. The other terminals of these coils, as shown, are connected to a buss wire 52 which latter is connected to the lead 43 constituting one side of the energizing line, while the stationary contacts, of the several push buttons at the floors and the several push buttons on the car are separately connected as groups in series to the lead 41 constituting the other side of this line. When a push button is operated, as for example the push button U--4, the stop 4'? of the corresponding coil 49, in this case the coil U--4, will be moved to the position shown by Fig. 1, so as to stop rotation of the shaft 29 when the parts come to the position in the drawings.

The motor 31 for turning the shaft 29 preferably is energized to initiate rotation thereof when any of the push buttons are operated. To this end, in the embodiment of the invention disclosed, the lead 43 which connects one terminal of all the coils 49 to one side of the line of the energizing source of electro-motive force, has inserted therein the energized winding of an electro-magnetic relay switch 53, Fig. 2. The contacts 55 of this switch serve by cooperation with leads 56, 57 and 58 to connect the energizing winding 59 of an electro-magnetic switch 60 across the leads 41, 43 when current is passed through the winding 53. The switch 60 when closed causes the motor 31 to operate and, when opened, causes the motor 31 to be de-energized. As shown, the motor 31 has a three-phase delta winding and is energized by' the leads 61 controlled by the switch 60. It

" will be observed, that as a result of this consistance winding so as to prevent damage to the,

motor when it is forcibly prevented from rotating by the selected stop 47.

Herein, for maintaining the selected stop 47 in position and for maintaining the motor 31 energized when the finger of the operator is removed from the push button which selects the stop to be actuated, each stop has associated therewith a switch 63, one contact of which is connected to the terminal of the coil connected by the leads 50, 51 to the movable contact of the corresponding push button, while the other contact of each coil is connected by a lead 64 to one of the brushes 65 at the releasing switch 33. These brushes 65 correspond in number to the push buttons, and in the drawings are marked with corresponding legends. Each brush makes contact with the periphery of a metal disk 67 fixed to rotate with the shaft 29 in insulated relation thereto, the disk being placed in electrical communication with the lead 41 by means of a brush 69 and lead 71. It will be observed that if one of the two push buttons U5, for example, is pressed to actuatethe corresponding stop 47 and switch 63, the closure of the latter will maintain the circuit through the corresponding coil 49 when the finger of the operator is removed from the push button.

As shown, the disk 67 carries a segment 73 insulated at 7.5 from the body of the disk, this segment being connected by a lead 77, contact ring 79 and brush 81 and lead 83 to one contact of an electro-magnetic relay switch 85, theother contact of which is connected by a lead 86 to the lead 41. The electro-magnetic switch 85 is controlled by a coil 87 energized by the potential in the bridge circuit connected to the brush arm 23. Under high potential conditions in the bridge circuit, the switch 85 will be closed, but, when said potential falls to or approaches zero or other predetermined value, the coil winding 87 will be de-energized to permit the switch 85 to open, which will break the circuit through the coil 49 for actuating the stop at that time in stop position, and also break the circuit through the energizing coil of the relay switch 53 for controller motor 31, so that said stop will be withdrawn and the controller motor will be de-energized as the elevator car reaches the selected floor.

If desired, for preventing movement of the elevator while discharging passengers when the car reaches the selected floor, which movement might be caused by operation of a push button at some other floor, the elevator doors maybe associated with suitable switch devices connected in series in the lead 21, which devices, when a door is open, will interrupt the electrical continuity of the lead 21 and prevent operation of the elevator hoisting motor 7. Conveniently to the same end, the switch 85 has associated therewith a dash pot 89 for delaying opening of the switch 85 for a predetermined period after the car has stopped at the selected floor, so as to insure that the car will come to a stop at the selected floor and the door may be opened.

Herein the elevator hoisting motor 7, which as indicated is of the three-phase delta-wound type, is energized by leads 91, and is controlled by a high current electro-m-agnetically operated two-pole double-throw reversing switch 93 situated on the main control panel 95. As shown, one of the leads 91 is connected with the motor winding at the point 97, while the other leads are respectively connected to the upper and lower pairs of or posed contacts 99 and 101 of the switch.

and lower coils 113 cooperating with suitablearmatures 114 so that when the upper coil is energized the switch blades will be depressed and when the lower coil is energized the switch blades will be raised. It will be observed that, when the switch blades are depressed, the middle lead 91, as shown in the drawings, will be connected to the point 107 on the motor while the left hand lead 91 will be connected to the point 103, but that when the switch blades are raised, these connections are reversed. Consequently, by energizing one or the other of the coils 113, the motor 7 may be rotated in either of opposite directions to raise or lower the elevator car.

As shown, the reversing switch 93 is controlled by a low potential reversing relay switch 115, which is actuated electro magnetically under the joint control of the reverse switch 32 and a single pole double-throw reverse current relay 117. As shown, the coils 113 of the switch 93 each have one terminal connected by leads 119 and 86 to the lead 41 which constitutes one side of the line leading from a suitable source of energizing electro-motive force. The other terminals of these coils are respectively connected by leads 120 to the upper and lower pairs of contacts 121 of the reversing relay switch 115. The lead 43, which constitutes the other side of the line, connected by a lead 122 to the brush arm 123 of the reverse switch 32, said switch having a contact segment 125 cooperating with said brush arm and connected to the inner pair of contacts 127 of the switch 115, while the other contact segment 129 of said switch 32 is connected to the outside contacts 129 of said switch 115.

The brush arm 123 is positioned to connect the leads 43 and 122 with the contact segment 125 when the elevator is to be moved upward and positioned to connect said leads with the contact 129 when theelevator is to be moved down. It will thus be observed that if the switch 115 is energized; as hereinafter described, to raise the switch blades 131 thereof, and the switch arm 123 is in the position of the parts shown by'Fig. 2, the lower coil 113 of the switch 93 will be energized to raise the blades 111 of that switch so as to cause the motor 7 to rotate in one direction, while, if the switch arm 123 is moved to contact with the segment 129, the upper coil 113 instead of the lower coil of the switch 93 will be energized to depress the blades 111 which will cause the motor 7 to rotate in the opposite direction. It will be also observed that, if the switch 115 had been energized to depress the blades 131 thereof, under these conditions, in each instance the direction of rotation of the motor 7 would have been opposite to that mentioned, and hence it will be observed that reversal of either the switch 32 or 115 will cause. a reversal in the direction of rotation of the motor 7.

The switch 115, as shown, is provided with energizing coils 133 cooperating with suitable armatures for raising and depressing the blades 131 of that switch. Herein, one terminalof eachof nected by leads 136 to the opposed contacts 137 of the reverse current switch 117. The reverse ourrent switch has a swinging armature 139 connected by a lead 141 to the lead 119, the latter connected to the lead 41 constituting one side of the line for energizing the relays. Consequently, when the armature 139 is swung to the right to contact with the right hand contact 137, the lower coil 133 of the reversing relay switch 115 is energized to raise the switch blades 131, and thus cause the motor 7 to rotate in one direction for a givenposition of the reverse switch 32, while,

if said armature is moved to the left to contact with the left hand contact 137, the upper coil 133 will be energized to cause the switch blades 131 to be depressed and the motor 7 to rotate in-the opposite direction.

Herein, the purpose of the reverse current switch 117 is to operate to reverse the motor- 7 through the reversing relay switch 115 and motor reversing switch 93 if the car should travel past the selected floor. As shown, to this end the bridge circuit 21 has in series therewith the primary winding 155 of an input transformer 157 ofan amplifying device, the latter provided with an output transformer 159, the terminals of the secondary winding 161 of which latter are connected to leads 163 for energizing the reversing coil 151 of the reverse current switch. Cooperating with the swinging armature 139 of the reverse current switch is a magnetizing coil 165 connected by the leads 119 and 135 to opposite sides of the line 41, 43. The coil 151 which surrounds the lower portion of the armature 139 is inclined to the latter at about 45 degrees and consequently the field created by said coil has poles at opposite sides of said armature. The current flowing through the'coil 151 and the coil 165 being in phase or oppositely out of phase, because they are in effect connected to a common source of electro-motive force, will cause an instantaneous relation between the field of the electro-magnetic armature and the field of the coil 151 which will hold the armature in contact with one or the other of the right and left hand contacts 137.

However, if the car should travel past the select- 9 stantaneous direction of current flow through the coil 151 will be reversed, which will cause a reversal in this instantaneous field relation, with the result that the armature 139 will swing to the opposite side of its travel so as to energize a different coil of the switch 115 and cause themotor 7 to reverse by reason of the consequent action on the switch 93. The amplifier for the potential of the bridge circuit may be of any convenient type, and herein is illustrated as a conventional A. C. operated transformer-coupled amplifier of the audion type. It will be observed that the amplifier causes a steeper voltage gradient in the output circuit of the amplifier than in the input circuit thereof, with the result that a larger current is maintained in said output as the bridge circuit approaches zero potential condition than would be possible without the amplifier, making it possible more conveniently to actuate the relays in the output circuit closer to zero potential.

As illustrated, the leads 163 at the output side of the amplifier also serve to energize 'a slowdown relay switch 167 and a stop relay switch 169,

connected by appropriate leads to terminals on the main control panel 195 for respectively actuating a known type of apparatus for causing slowing down andstopping of. the elevator motor as the carv approaches the selected floor. It will be observed that, when the coils associated with these switches are energized consequent upon movementpf the brush arm 23, the switches will be closed, and, that as the potential in the bridge circuit approaches zero potential condition, these switches will be successively deenergized to cause them to open successively and successively cause slowing down and stopping of the motor '7. The slow-down and stop circuits may be of any convenient kinds commonly employed in the art, which circuits in usual practice cause a contactor to open at the main control panel for placing resistance in the motor circuit when the elevator is to be slowed-down, and cause deenergization of the motor and the application of a. brake to the elevator hoisting drum when the latter is to be stopped.

It will be observed that the motor 31 and vari-v ous switches actuated thereby, together with the amplifier and relay switches 85, 115 and 117, may be located at any convenient point in the building.

' It will be observed that in the present embodiment of the invention it is unnecessary that a subscriber at a landing know the relative position of the car with respect to that landing. The subscriber merely pushes the fup or down button, depending upon whether he wishes to travel up to a higher floor or down to a lower floor, and the car will ultimately come to him. The reason for having an up bottom and a .down button at each landing between the top and bottom landings is, that if the subscriber wishes, for example, to'go up to a higher floor and pushes the up button, and the car at that time is moving downward at any part of the building, the car will answer all the down calls corresponding to landings below the car before it starts up to the subscriber. This action occurs because the selector arm 45 must always move in a clockwise direction in the present embodiment of the invention, and therefore must answer all the calls ahead of it before it answers a given call. For example, if the selector arm 45 is at D-3 and the D2 button is pushed the arm will stop at D -2 after it is released from D-B and must be released from the latter before it can move to U-4. It will be noted that by making the car, when it is moving down, for example, respond to all the down buttons below it before it can respond to any of the -up buttons, time is saved in operating the car and transporting the various subscribers to and from different floors.

In respect to the coordination between the reversing switch 32 and the reverse current relay 117, it will be noted that if the car is above a given floor, and the up button at that given floor is pushed, the current flow through the bridge circuit 21 will be in the opposite sense to the current flow that would exist if the car were below that floor. When the switch arm 123 is on-the up segment it will control the connections to the switch 115 to cause the latter when operated to effect movement of the main motor switch 93 is one direction provided the arm 139 of the switch 117 is thrown to the right, and will reverse the connections to cause the switch 93 to move in the opposite direction if the arm 123 is on the ,down segment under these conditions, but in each case the switch 93 will be moved in the opposite direction if the arm 139 is thrown to the left. The direction of travel of the elevator motor is dependent upon whether the switch 93 is in its up or down position as shown in the drawings, and therefore the direc tion of travel of the car when the arm 123 is on the up segment depends upon the direction of the flow of current through the bridge circuit, that is to say, if, for example, the arm 123 is at the position which corresponds to U-4, as shown in the drawings, and the car is at the third floor, the how of current through the bridge circuit will be in the opposite direction to what it would be if the car were at the fifth floor. In both cases the switch arm 123 causes the same contacts of the switch 115 to be energized, but the switch 117 determines the direction in which the switch 115 is thrown and in one case causes the switch 115 to be in its down position and in the other case in its up position. It will be noted that if the car travels past the given floor this same action occurs, namely, the current through the bridge circuit is reversed to cause the elevator motor to be-reversed, and thereby the car is automatically leveled. This action occurs whether the direct or alternating current is employed, because when alternating current is employed the direction of the flow of current in the bridge circuit is reversed in respect to its instantaneous value as compared to the instantaneous value of the current controlled by the switches 32, 115 and 93 which are directly connected to the line 43.

It will be understood by those skilled in the art that the elevator hoisting mechanism moves and operates conjointly with the car, and that, although in the embodiment of the invention illus trated the elevator control system is directly responsive to and directly controlled by the motion and position of the car, it may be indirectly rcsponsive to and controlled by this motion and position by having itresponsive to and controlled by the elevator hoisting mechanism, or by any auxiliary device or attachment connected to the car or hoisting mechanism to move conjointly therewith. For example, as will be understood by those skilled in the common expedients of the art, where building conditions, local laws, or other considerations do not permit the installation of the variable resistance comprising the wire 9 extending the length of the shaft and the sliding contact 11 on the car, as shown in the drawings, the same may be substituted by an electrically equivalent variable resistance placed elsewhere in the building and connected to the car or ele vator hoisting mechanism to operate conjointly therewith. Consequently in the appended claims, Where the context permits, by responsive to" and controlled by the position and motion of the elevator car, and by words of like import, are comprehended both direct and indirect response to or control by the motion or position of the car and its associated hoisting mechanism.

I claim:

1. An electric elevator system having, in combination, power-actuated means for moving an elevator car to a predetermined position, a system of resistances connected in series-parallel to a source of electro-motive force and having a circult bridged across the resistances in series to form a so-ealled Wheatstone-bridge, controlling means for said power-actuated means responsive to predetermined electrical potential conditions across said bridge circuit, means responsive to motion of said car for varying the resistance ratios at one side of said system, and means for selecting predetermined resistance ratios at the other side of said system.

tions, a series of resistances connected in seriesparallel to a source of electro-motive force, and having a circuit bridged across said resistances in series to form a so-called Wheatstone-bridge, means responsive to the electrical potential conditions across said bridge circuit for controlling said power-actuated means, means for varying the resistance ratios at one side of said system in response to-motion of said car, and operator controlled means for selecting predetermined resistanceratios at the other side of said system.

3. An electric elev tor system having, in combination, power-actu ted means for moving an elevator car to any of a plurality of selected positions, a series of resistances connected in seriesparallel to a source of electro-motive force, and having a circuit-bridged across said resistances in series to form a so-called Wheatstone-bridge, means responsive to the electrical potential conditions across said bridgecircuit for controlling said power-actuated means, means for varying the resistance ratios at one side of said system in response to motion of said car, and means including selective switches for varying the resistance ratios at the other side of said system.

4. An electric elevator system having, in combination, power-actuated means for moving an elevator car to'any of a plurality of selected positions, a series of resistances connected in seriesparallel to a source of electro-motive force, and having a circuit bridged across said resistances in series to form a so-called Wheatstone-bridge, means responsive to the electrical potential conditions across said bridge circuit for controlling said power-actuated means, means for varying the resistance ratios at one side of said system in response to motion of said car, motor-operated means for varying the resistance ratios at the other side of said system, and means including selective switches for controlling said motor operated means.

5. An electric elevator system having, in combination, power-actuated means for moving an elevator car to any of a plurality of selected positions, a series of resistances connected in seriesparallel to a source of electro-motive force, and having a circuit bridged across said resistances in series to form a so -called Wheatstone-bridge,

means responsive to the electrical potential con-- ditions across said bridge circuit for controlling said power-actuated means, means for varying the resistance ratios at one 'side of said system in response to motion of said car, motor-operated means for varying the resistance ratios at the other side of said system including stop devices for determining the positions of adjustment of said means, and selective switch means for controlling said motor-operated means and said stop devices.

6. An electric elevator system having, in combination, power-actuated means for moving an elevator car to any of a plurality of selected posi tions, a series of resistances connected in seriesparallel to a source of electro-motive force, and having a circuitbridged across said resistances in series to form a so-called wheatstone bridge, means responsive to the electrical potential conditions across said bridge circuit for controlling said power-actuated means, means for varying the resistance ratios at one side of said system in response to motion of said car, means including tive switch means for energizing said motor and ,for actuating said stopdevices, and means controlled by the potential of said bridge circuit for deenergizing'said motor and stop means when said car is moved to a selected position.

7. An electric elevator system having, in combination, power-actuated means 'for movingan elevator car toariyof a plurality of selected positions, a series of resistances connected in seriesparallel to a source of electro-motive force, and having a circuit bridged across said resistances in series to form a so-called Wheatstone-bridge, means responsivetothe electrical potential conditions across'said bridge circuit for controlling said power-actuatedmeans, means for varying the resistance ratios atone side of said system in response to motion of said car, motor operated means for varying the resistance ratios at the other side of said system including stop devices for determining the positions of adjustment of said means, selective switch means for controlling said motor operated means and said stop devices, and means controlled by the potential of said bridge circuit for moving said stop devices into non-stop positions when said car is moved to its selected positions.

8. An electric elevator system having, in combination, power-actuated means for moving an elevator car to any of a plurality of predetermined positions,- a system of resistances connected in series-parallel with a source of electro-motive force and having. a circuit bridged across the resistances in series to forma so-called Wheatstonebridge, switch means responsive to the current flow in said bridge circuit as determined by the relative values of the ratios of resistances at opposite sides of said system for controlling said power-actuated means for causing motion of said car in either of opposite directions, and means responsive to movement of said car for varying the resistance ratios at one side of said system, and means for selectively varying the resistance ratios at the other side of said system.

9. An. electric elevator system having, in combination, power-actuated means for moving an elevator car to any of a plurality of predetermined positions, a system of resistances connected in series-parallel with a source of electro-motive force and having a circuit'bridged across the resistances in series to form a so-called Wheatstonebridge, motor controlling means responsive to thecurrent flow in said bridge circuit as determined by the relative ratio of resistances at oppomoving an elevator car to any of a plurality of predetermined positions, a system of resistances connected in series-parallel with a source of electro-motive force and having a circuit bridged across the resistances in series to form a so-called Wheatstone-bridge, motor controlling reversing switch means responsive to the current flow in said bridge circuit as determined by the relative values of the ratios of resistances at opposite sides of said system for moving said car'by said motor in either of opposite directions, means for selectively adjusting the resistance ratios at one side of said bridge circuit, and means responsive to the motion of said car for varying the resistance ratios at the other side of said bridge circuit.

11. An electric elevator, system having, in combination, means including an electric motor for moving an elevator car to any of a plurality of predetermined positions, a system of resistances connected in series-parallel with a source of electro-motive force and having a circuit bridged across the resistances in series to form a so-called Wheatstone-bridge, motor controlling reversing switch means for determining the direction of movement of said car by said motor, actuating means for said reversing switch responsive to the current flow in said bridge circuit as determined by the relative values of the ratios of resistances at opposite sides of said system, selective reversing switch means cooperating with said actuating means, means for selectively adjusting the resistance ratio at one sideof said bridge circuit and for selectively actuating said selective reversing switch, and means responsive to the motion of said car for varying the resistance ratios at the other side of said system.

12. An electric elevator system having, in combination, means including an electric motor for moving an elevator car to any of a plurality of predetermined positions, a system of resistances connected in series-parallel with a source of electro-motive force and having a circuit bridged across the resistances in series to form a so-called Wheatstone-bridge, motor-actuated means having a plurality of positions of adjustment for varying the resistance ratios at one side of said system, magnetically operated stop devices for each of said positions of adjustment of said motoroperated means, circuit means including selective switches for actuating said stop devices into stop positions, relay means actuated when said stop devices are so actuated for maintaining the latter in stop positions, means for varying the resistance ratio at the other side of said system in response to motion of said car, and means including a switch actuated in response to the potential across said bridge circuit for causing said stop devices to move to non-stop positions when said car is moved to its selected position.

13. An electric elevator system having, in combination, a resistance strip arranged lengthwise of the elevator shaft, a sliding contact on the car cooperating wtih said strip, resistance means connected in parallel with said strip to a source of electromotive force, bridge circuit means for connecting said contact to said resistance means intermediate the points of connection of the latter to said source of electromotive force, means including selective push buttons for changing the ratios of the resistances in circuit at each side of the point of connection ofsaid contact to said resistance means, a car hoisting motor, and means responsive to the potential across said bridge circuit means for controlling said motor.

14. An electric elevator system having, in combination, a resistance strip arranged lengthwise of the elevator shaft, a sliding contact on the car cooperating with said strip, resistance means connected in parallel with said strip to a source of electromotive force, bridge circuit means for connecting said contact to said resistancemeans intermediate the points of connection of the latter to said source of electromotive force, means including selective pushbuttons'for changing the ratios of the resistances in circuit at each side of the point of connection of said contact to said resistance means, a car hoisting motor, and means responsive to the potential across said bridge circuit means for controlling said motor including relay switch devices energized thereby for stopping said motor as said potential approaches zero potential.

15. An electric elevator system having, in combination, a resistance strip arranged lengthwise of the elevator shaft, a sliding contact on the car cooperating with said strip, resistance means connected in parallel with said strip to a source of electromotive force, bridge circuit means for connecting said contact to said resistance means intermediate the points of connection of the latter to said source of electromotive force, a car hoisting motor, means including selective pushbuttons for energizing said motor and selectively changing the ratios of the resistances in circuit at each side of the point of connection of said contact to said resistance means, and means responsive to the potential across said bridge circuit means for stopping said motor as said potential approaches zero potential.

16. An elevator system having, in combination, resistances connected to a source of electromotive force in series parallel with a circuit bridged across said resistances in series to form a socalled Wheatstone-bridge, means responsive to the potential across the bridge circuit for successively operating circuit controlling means for slowing down and stopping the car, means for selectively varying the ratio of resistances at one side of said bridge circuit, and means for varying the ratio of resistances at the other side of said bridge circuit in response to motion of said car. 110

1'7. An elevator system having, in combination, resistances connected to a source of electromotive force in series parallel with a circuit bridged across said resistances in series to form a so-called Wheatstone-bridge, said resistances including a 115 resistance strip arranged lengthwise of the elevator shaft, means responsive to the potential across the bridge circuit for successively operating circuit controlling means for slowing down and stopping the car, means for selectively varying the ratio of resistances at one side of said bridge circuit, and means for varying the ratio of resistances at the other side of said bridge circuit in response to motion'of said car.

18. An elevator control having, in combination, a system of resistances connected to form two sets of resistances in series with the two series in parallel with a source of electromotive force, circuit means for controlling slow down and stop means for the elevator car, means for connecting 130 said circuit means at opposite ends thereof to said sets of resistances intermediate the points of connection of said sets to the source of electromotive force, said last mentioned means having provision for selectively varying at the will of the operator the ratio of the resistances of one set at opposite sides of the point of connection of said circuit means to said set and for selectively varying in response to motion of the car the ratio of the corresponding resistances of the other of said sets.

19. Leveling means for an elevator having, in combination, a reversing means for the elevator car; circuit means for controlling said reversing means comprising means forming a pair of resistances or variable ratio A, means for varying said ratio A in response to the position or the elevator car, means forming a second pair of resistances of variable ratio B, means for varying said ratio B by the operator; said reversing means 150 being responsive to current flow conditions produced in said circuit means as determined by the algebraic sign of A minus B, and stop means for said car responsive to current flow conditions in'said circuit as determined by a predetermined arithmetical difference between A and B.

20. Leveling means for an elevator having, in combination, an elevator hoisting motor, a reversing switch means for said motor; apparatus comprising circuit means for controlling said switch means; said circuit means comprising means forming a pair of resistances of variable ratio A, means for varying said ratio A in response to the position of the elevator car, means forming a second pair. of resistances of variable ratio B, means for varying said ratio B by the operator; said reversing switch means being responsive to 0 rent flow conditions produced in said circuit means as determined by the algebraic sign of A minus B, and stop means for said motor responsive to current flow conditions in said circuit means as determined by a predetermined arithmetrical difference between A and B.

21. Leveling means for an elevator having, in combination, an elevator hoisting motor, a reversing switch 'meansior said motor; apparatus' comprising circuit means for controlling said switch means; said circuit means comprising means forming a pair or resistances of variable ratio A, means for varying said ratio A in re-'- sponse. to the positionof the elevator car, means forming a second pair oi. resistances of variable ratio B, means for varying said ratio B by the operator; said reversing switch means being responsive to current flow conditions produced in' said circuit means as determined by the algebraic sign of A minus B, operator controlled means for reversing the direction of rotation of said motor determined by said. algebraic sign of A minus B, and stop means for said motor responsiveto current flow conditions in said circuit means as determined by a predetermined arithinetical difference between A and B.

22, An elevator control system having, in combination, operating means for raising and lowering an elevator car, control means for said operating means comprising motor-stoppingswitch means responsive to a predetermined electrical potential, a circuit including a potential amplifier for impressing the electrical potential on said switch means, and means responsive to the position of said car for impressing a variable potential on said amplifier. I

23. An elevator control system having, in combination, operating means for raising and lowering an elevator car, control means for said operating means comprising motor-stoppingoperating ,rneans comprisi g motor-stopping-" switchmeansresponsive to a predetermined electrical potential, a circuit including a potential amplifier or 'the'electronic type tor'impressing fine af-"i651 potential on switch means,

said amplifier having a control grid, means responsive to the position or said car for impressing a variable potential on said grid, and means controlled by the operator for determining the position oi said car at which it causes said amplifier to impress on said switch means ,said predetermined potential. 1

25. An elevator control system having, in combination, operating means for anelevator car, electrically'actuated control means for said operating means, resistances the ratio of which is controlled by the operator, other resistances the ratio or which is varied in response to the position of the car, an electronic amplifier for energizing said control means, said amplifier having a control grid, and circuit means for impressing a potential on said grid, and means for impressing a potential on said circuit means proportional to the difference in said ratios of said resistances.

26. The combinaton with an elevator car of circuit means, means for controlling the potential impressed on said circuit means comprising a source of electromotive force, means forming two resistances connecting one end of said circuit means toopposite sides respectively of said source of electromotive force, means forming two resistances connecting the other end of said circuit means to opposite sides respectively of said source or electromotive force, means controlled by the operator for-varying the resistanceratio of said two resistances connected to one end of said ciroi the elevator car for varying the resistance ratio "of the other two resistances.

27. The combination with an elevator car of an electrical device to be controlled conjointly by the operator and the car, means for impressing an electrical potential on said device comprisf ing an amplifier, circuit means for impressing the input potential on said amplifier comprising a source of electromotive force, means forming two resistances connecting one end of said circuit means to opposite sides respectively of said source or electromotive force, means forming two-resistances connecting the other end of said circuit means to opposite sides respectively of said source of electromotive force, means controlled by the operator for varying the resistance ratio of said two resistances connected to one end of said circuit means, and means controlled by movement of the elevator car for varying the resistance ratio of the other two resistances.

28. The combination with an elevator car of an electrical device to be controlled conjointly by the operator and the car, means for impressing an electrical potential on said device comprising an amplifier of the electronic type having a control grid, circuit means for impressing a potential on said grid comprising a source of electromotive force, means forming two resistances connecting one end of said circuit means to opposite sides respectively of said source of electromotive force,

means forming two resistances connecting the other end of' said circuit means to opposite sides respectively of said source of electromotive force, means controlled by the operator for varying the resistance ratio of said two resistances connected to 'one end of said circuit means, and means.con-

trolle by movement of the elevator car for vary ing e resistance ratio or the other two resistances.

{HAROLD J. GRAHAM. 

